DESCRIPTION: Leakage of radioactive material away from the injection site reduces therapeutic efficacy, induces undesirable damage to normal tissues, and increases the risk of side effects (dermitis, neuritis) and secondary neoplasia (leukemia and osteosarcoma). Insoluble glass or ceramic microspheres may contain radioactivity to the injection site and inhibit leakage, but may also later induce inflammation, deterioration of tissues, and fibrosis, or cause physical damage to healing/healed joints. These obstacles may be overcome with a new, timed- bioresorbable calcium phosphate microspheres. These microspheres can be made to maintain structural integrity for 30 days (11 physical half- lives for Y-90, i.e., decayed to negligible activity) before they begin to dissolve at a predetermined rate, leaving nothing in the patient to cause irritation, blockage or physical damage. The purpose of this project is to prepare and test Y-90-containing microspheres with pre- programmed bioresorption. Glass composition range and Y-90 solubility in glasses will be established. The in vitro properties of bioresorbable Y-90 calcium phosphate glass microspheres will be characterized so that follow-up tests can be conducted in laboratory animals. Applications of Y-90 microspheres include direct intratumoral injection (infusional brachytherapy) in treatment of cancers of liver, pancreas, brain, etc., and radiation synovectomy of rheumatoid arthritis.